2.7L Stalls infrequently, no CEL.

Greetings,
I have a 98 2.7L with 230000 miles, automatic. A few months ago, it started stalling when I came to a stop or let off the throttle traveling at speeds <25. In addition, when I am driving on the freeway and take my foot off the gas pedal, the truck sometimes downshifts out of O/D briefly. I have since inspected the vacuum lines, cleaned the air filter, replaced the fuel filter, replaced the IAC valve, replaced the exhaust manifold gasket (it was shot, leaking exhaust into the engine compartment), and about every standard troubleshooting procedure I know of. After all of this, the engine stalls far less frequently, runs smoother, and is a tad faster, nonetheless, it still stalls.

I am thinking at this point I am dealing with a throttle position sensor or a torque converter/transmission valve/solenoid issue.

The truck is not throwing any CELs and otherwise drives great.

Does anyone out there have experience with such issues?
Thanks,
Ian

 

Have you ever replaced the timing chain?

 

No, I haven't replaced the timing chain, but I've considered it as a cause. If it was the chain, could it be so worn and not throw a cel? Also, could the the chain be causing the random down-shifting too?

 

have you tried cleaning throttle body, i had the same issue with a chevy and that took care of it.

 

Yes, throttle body removed and cleaned. IAC valve replaced.

 

zeroian, I believe that yes, the timing chain could be worn just enough to stall, yet not throw a CEL. I expect that the downshift is caused by this as well. Just as you would downshift a manual transmission to compensate for a load change, the computer is telling transmission to shift as well. You have eliminated fuel and air as a source of the problem it sounds.That only leaves timing.

 

I have cold stalling
and lack of power

'98 2.7 stick
within the past two months
so far I have changed with new toyota parts :
IAC valve (cleaned throttle body passages )
MAF sensor
TPS sensor
ECT sensor
EGR vacuum modulator
spark plugs and wires
air filter
in tank and inline fuel filters
fuel pump
fuel pressure regulator
ECM computer (toyota remnan)

double checked and/or cleaned these parts:
EGR VSV
EGR valve
catalytic converter
muffler
triple checked for vacuum leaks (even at PSump and brake booster)

gave up and took it to toyota dealer for the $100 diagnosis said compression was 140-150-180-190, they could not find anything after 5 hours and said it needs the head tore off
took it to another local mechanic, they checked, timing, fuel pressure and IAC couldnt find anything and suggested valve job

I pulled the head today and put the cams back in and the valves dont look too bad on the bench
cam chain looks tight
first line up between valve marks and balancer marks was 5 degrees off , turned it over clockwise 360 and it came up dead zero TDC , with the cam dots together so cam timing seems good

maybe head gasket leaking between cylinders ?
cylinders look real good , no scoring doesnt use ANY oil in 10,000 miles

I shook the cam chain real hard at the links and cant find play
the adjuster was about in the middle of its range and sliding smoooth, ratchet holding

started raining (no garage)


now what !
just put it back together ?

 

Before you spend another dime on your Tacoma, check your frame carefully for rust through. 98s are part of the Toyota buy back for frame rust.

As for the head gasket, is there any visible signs on the block or head of leaking?

 

another dissapointment : no signs of a break in the sealant between cylinders
the valves look old and nasty but Ive seen worse
I am wondering if the tech at the toyota dealer did the comp check wrong , removing one plug at a time \anyway , I paid for dignosis and got three opinions that bad valves are the cause of the stalling because the engine control system cannot compensate

Im in Californica, no rust on the frame that I can find
I'll look again but it sure will be a first to ever be compensated for anothers goof, win a prize, or get a windfall
everything in life is a bizarre grunting uphill struggle just like this nightmare lemonota
I would never imagine getting market value from toyota for this swayback weak POS, I could more likely imagine winning the lottery

 

If you dont mind me asking ... how did you check/ clean the cat? JW


Ian ( op )
Have you made sure your trans fluid is toped off and not super low ?
could cause the torque converter to not disengage at stops causing the stall

 

update on mine
I replaced the head, all new parts , and it runs like new now

no more cold stalling
waymore power uphill
real smooth idle

 

not aware of a cleaning method but you can take it off and you should be able to see straight through the honeycomb easily

 

ahhh.. of course the ole peak down the pipe trick , lol


what you gunna do with your old head hmmmmmmmmmmmmmmmmmmmm?

 

$100 + shipping
with cams , cams look excellent, no cracks or stripped threads, probably needs 4 ex valves

 

^ pmed